This invention relates generally to lasers utilizing a gaseous lasing medium and more particularly to methods and apparatus for improving the operation and cooling thereof. The term "gaseous medium" is used herein to include gases, vapors, and mixture thereof.
In the typical high-power gas laser, an electric discharge or other energy source initiates lasing, which is accompanied by an abrupt increase in the temperature of the gas and by severe gas disturbances, such as shock waves and sound waves. As much as 97% of the power input to the laser may be dissipated as heat. Most of this heat from the high-power laser is removed by a cooling fluid which is circulated about the outside of the laser tube. Before the laser can be re-fired, the gas must be cooled so that the electrons again are at their ground-energy state and the above-mentioned disturbances minimized. Typically, this is accomplished by gas-purging the high-power laser tube several times. The typical purging operation comprises (a) circulating the gas discharge from the laser through an external loop including a blower, a heat exchanger, and flow-straightening means (such as metal guide vanes) and (b) re-directing the conditioned gas through the laser. It would be advantageous if the transfer of heat from the laser gas to the laser-tube coolant could be accomplished more efficiently; this would result in an increase in the laser power output. It would also be advantageous if the transfer of heat could be accomplished by a technique which acts to suppress laser-gas disturbances immediately after firing of the laser occurs.
The following article describes the use of a forced-vortex heat exchanger to cool a gas as it flows through an infrared-detector tube: J. M. Nash, "Vortex Heat Exchanger Cooling for IR Detectors," Applied Optics, Vol. 14, No. 12 (December 1975). The described vortex heat exchanger comprises an annular device which is closed at one end and is provided with a diffuser at its other end. Air is introduced tangentially near the closed end and forms a vortex which swirls about the exterior of the detector tube. However, unlike the standard vortex tube, the vortex heat exchanger is connected to a diffuser, allowing the temperature and pressure at the core of the vortex to be much lower than at either the tube inlet or at the periphery (outer circumference) of the vortex. The article states that the provision of a diffuser at the laser-tube outlet markedly increases the efficiency of the vortex tube because it permits the pressure at the center of the vortex to fall below atmospheric without inflow occurring.
The following publication describes a gas laser which is provided with internal spiral heat-exchange fins for directing the laser gas along helical multiple-flow paths while cooling the gas: Laser & Applications (September 1982), page 96. The spiral fins periodically direct the gas flow through the electrical discharge, which extends along the laser wall; that is, the discharge path is laterally offset from the central opening defined by the fins. The publication states that the fins provide more efficient heat transfer and a longer gas flow path than are obtained in axial-flow lasers. As a result, a given volume of gas is used more effectively, providing an increase in power output for a given laser length.
The use of forced-vortex flow to air-cool a solid laser is described in the following article: Soviet Journal of Optical Technology, Vol. 35, No. 1, January-February 1968. In that arrangement, the air vortex flows about the exterior of an elongated lasing body, or crystal.
As used herein, the terms "forced-vortex" and "forced-vortex flow" refer to a vortex having a longitudinal axis and circular motion, the circular vortex motion about the axis being that of a rotating solid cylinder.